1. Field of the Invention
This invention relates to the drilling and workover of wells penetrating subterranean reservoirs, particularly high temperature reservoirs, and more particularly to the drilling and workover of such reservoirs with foam drilling fluids.
2. Description of the Prior Art
It has long been conventional practice in the drilling of bore holes penetrating subterranean reservoirs to circulate a drilling fluid down the drill pipe and back up the bore hole annulus for the removal of debris and drill cuttings from the bore hole. Drilling fluid also serves to prevent sloughing in the bore hole during the drilling operation. Recently, air or other gases have replaced conventional drilling fluids in the drilling of some bore holes, and have proved particularly beneficial in reservoirs wherein dense conventional drilling fluids would be lost to the formation. Additionally, gases have also provided longer bit life and higher rates of penetration in the drilling of bore holes.
However, in many reservoirs, water enters the bore hole from adjacent water-containing strata; and gases have proved unable to remove this water. In view of this problem, foams have been developed to remove both the cuttings and the water from these bore holes. Numerous foam compositions have been proposed and used; however, as yet, foams have not been satisfactorily used in the drilling and workover of wells penetrating high-temperature subterranean reservoirs, such as geothermal reservoirs.
At present, geothermal reservoirs are drilled using air or other gases as the drilling or workover fluid. This is particularly true in the vapor-dominated geothermal reservoirs wherein the low bottom-hole pressure precludes the use of heavy drilling fluids, such as conventional drilling muds. If used, circulation of these conventional drilling fluids would quickly be lost to the low-pressure reservoir. Also, the high temperature of the geothermal reservoirs have precluded the use of foams normally used in the typically low-temperature, oil-bearing reservoirs. While the temperature of typical oil-bearing reservoirs amenable to foam drilling may reach as high as 200.degree. F., the geothermal wells now being drilled have bottom-hole temperatures of from about 400.degree. F. to about 700.degree. F. Because these high-temperatures greatly reduce foam stability, foams have not been used extensively as drilling or workover fluids in wells penetrating high-temperature subterranean reservoirs, such as wells penetrating geothermal reservoirs.
A wide variety of compounds are known to have detergent and foam-forming capabilities. For example, McCutcheon's Detergents and Emulsifiers, North American Edition, 1973 Annual, page 193, describes various betaine compounds as foam stabilizers and detergents. The same publication at page 26 describes various sodium linear alkylate sulfonates as liquid detergent bases.
U.S. Pat. No. 3,318,379 to Bond et al. describes a secondary recovery process in which a bank of foam is formed in situ and driven through the reservoir. Listed among a large group of surface active agents which can be used alternatively to generate the foam are Product BCO identified as C-cetyl betaine and Petrowet R identified as sodium alkyl sulfonate.
When a foam in a high temperature well contains air, or contacts and is contaminated by reservoir fluids containing air or oxygen, corrosion of the drill string, casing and other metal equipment contacted by the foam drilling fluid can occur.
U.S. Pat. No. 3,572,439 to Hutchison describes an ammoniated gas-in-liquid foam as a circulation fluid, e.g., drilling fluid, in wells. The ammonia enables the foam to be used in low velocity circulation. The foam is preferably preformed and generated using a concentrate which contains water, any foaming agent, for example lauryl sulfonate, or C-cetyl betaine, and ammonia or ammonium hydroxide.
U.S. Pat. application, Ser. No. 683,092, by Fischer and Pye filed May 4, 1976, now U.S. Pat. No. 4,092,252, discloses a foam drilling fluid containing, in part, a foaming agent and ammonia to provide corrosion protection in the vapor phase.
The various methods of the foregoing references have met with some success. However, many corrosion inhibitors were found to decrease the foam forming ability and/or foam stability of many foaming agents. Numerous combinations of corrosion inhibitors and foaming agents are not compatible.
Thus, there is a need for a drilling and workover method which employs a foam that is stable at high temperature, which can be used in high-temperature subterranean reservoirs and which is not affected by the presence of a corrosion inhibitor.
Accordingly, a principal object of this invention is to provide a method for conducting foam drilling and workover operations in high-temperature subterranean reservoirs.
Another object of this invention is to provide a method for conducting foam drilling and workover operations in high-temperature geothermal reservoirs.
Still another object of this invention is to provide a method for conducting foam drilling and workover operations in high-temperature subterranean reservoirs which employs a foaming agent that is stable at the temperatures encountered.
A further object of this invention is to provide a method for conducting foam drilling and workover operations in geothermal reservoirs which employs a foaming agent that is stable at the temperatures encountered.
A still further object of this invention is to provide such a method wherein the foam drilling fluid and workover fluid contain a corrosion inhibitor.
Other objects and advantages of this invention will become apparent to those skilled in the art from the following description.